VII. 9.7: A DAY IN THE LIFE OF FOOD

A. CARBOHYDRATES

3. Duodenum – amylase breaks down polysaccharides into disaccharides, brush border enzymes further break these down into monosaccharides

4. Absorption – large, hydrophilic monosaccharides are taken up by secondary active transport (goes with sodium ion flow); once the cells have high monosaccharide concentration, they flow out with facilitated diffusion into nearby capillaries

5. Storage – liver picks up these molecules and stores them for energy

B. PROTEINS

1. Mouth – chewing, but no digestion

2. Stomach – acid and pepsin hydrolyze peptide bonds

3. Duodenum – chyme is released into duodenum and stimulates release of CCK and secretin, which in turn causes GB to release bile and pancreas to release bicarb and other enzymes (trypsinogen is activated to trysin by enterokinase, which then activates other enzymes); these work on the tuna until all that is left are di- and tripeptides, which are hydrolyzed to AAs by brush border enzymes

4. Absorption – these freely diffuse into cells, where they are turned back into triglycerides, organized into cholymicrons, and travel via lacteals and the lymph system to finally reach the bloodstream

5. Storage – picked up by liver and adipose tissue (both have lipoprotein lipase), which breaks triglycerides back down into monoglycerides and free fatty acids

VIII. 9.8: VITAMINS

Vitamin

Function

fat soluble

A (retinol)

Visual pigment which changes conformation in response to light

D

Stimulates Ca++ absorption from the gut; helps control Ca++ deposition in the bone

E

Prevents oxidation of free fats

K

Necessary for formation of clotting factors

water soluble

B1 (thiamine)

Needed for enzymatic decarboxylations

B2 (riboflavin)

Made into FAD, electron transporter

B3 (niacin)

Made into NAD+, electron transporter

B6 (pyridoxine)

A coenzyme involved in protein and AA metabolism

B12 (cobalamin)

A coenzyme involved in the reduction of nucleotides to deoxynucleotides

C (acsorbic acid)

Necessary for collagen formation

Biotin

Prosthetic group essential for the transport of CO2 groups

Folate

Enzyme cofactor used in the transport of methylene groups; synthesis of purines and thymine; required for development of normal fetal nervous system